1. Field of the Invention
The present invention relates to a composite electronic device, in particular, a composite electronic device such as a laminated filter obtained by integrally firing a coil part composed of a coil conductor and a magnetic layer and a capacitor part composed of internal electrodes and a dielectric layer.
2. Description of the Related Art
A resistance (R), a capacitor (C) and an inductor (L) are passive elements in an electronic circuit, and each of them has a unique function. Furthermore, the passive elements can have functions that are different from the unique functions by being connected mutually. Hereinafter, the functions that are different from the unique functions caused by the connection between the passive elements can be referred to as circuit functions.
The plural passive elements can show the circuit functions by being connected with each other via wires, etc. after having been separately mounted on a printed circuit substrate, etc. However, there is a disadvantage that the mounting area of the passive elements increases when the passive elements are mounted separately. Therefore, it is required that the circuit functions are obtained by a single electronic device to meet a demand for downsizing various application apparatuses. A laminated LC filter is given as an example where the circuit functions are obtained by a single electronic device.
The laminated LC filter is composite electronic device in which the coil part and the capacitor part exist independently in a single unit. Here, it is necessary that the coil part composed of a coil conductor and a magnetic layer and the capacitor part composed of internal electrodes and a dielectric layer are superposed on each other and fired simultaneously to be sintered integrally to obtain the laminated LC filter. However, there were cases where the coil part and the capacitor part can not be sintered sufficiently integrally due to a difference of material between the coil part and the capacitor part.
In recent years, there have been attempts to interpose an intermediate material layer between the coil part and the capacitor part when manufacturing the composite electronic device comprising the coil part and the capacitor part.
Patent Document 1 discloses a LC composite device characterized in that a ceramic material prepared to be totally 100 mol % by incorporating 0.5 to 30 mol % of CuO into ZrO2, TiO2 or mixture thereof is interposed between a dielectric ceramic part and a magnetic ceramic part as an intermediate layer.
Patent Document 2 discloses a LC composite device characterized in that a ceramic composed of 15 to 40 mol % of BaO and 60 to 85 mol % of TiO2 and a glass contained in a dielectric ceramic part are disposed between the dielectric ceramic part and a magnetic ceramic part.
Patent Document 3 discloses a composite electronic device characterized in that an intermediate material layer includes FeZnCu based nonmagnetic ceramic and zinc borosilicate based glass.
Patent Document 4 discloses a bonding material for electronic device obtained by adding a ZnO—SiO2—B2O3 based glass to a composition composed of ZnO, BaO and TiO2.
Patent Document 5 discloses a composite electronic device characterized in that an intermediate material layer includes Zn—Ti material.
However, only the results in the specific dielectric ceramic materials are described in any of the Patent Documents 1 to 5. Therefore, it cannot be said that the techniques described in the Patent Documents 1 to 5 can be applied to any dielectric ceramics.
The dielectric ceramic part of the Patent Document 1 is composed of a Pb based composite perovskite material, and therefore is unfavorable from the viewpoint of environmental consideration. Further, in the Patent Document 1, a material which is sintered at 1000° C. at the time of integration is used. Therefore, Ag whose melting point is less than 1000° C. cannot used as a conductor material.
The dielectric ceramic part of the Patent Document 2 is composed of a material containing Pb, and therefore is unfavorable from the viewpoint of environmental consideration.
The intermediate material layer disclosed in the Patent Document 3 contains Fe. There are cases where characteristics of the dielectric ceramic part deteriorate due to a diffusion of Fe contained in the intermediate material layer at the time of sintering to the dielectric ceramic part depending on the material of the dielectric ceramic part.
The present inventors conducted a supplementary examination on the bonding material disclosed in the Patent Document 4. The inventors found that the material of the dielectric layer to which the bonding material disclosed in the Patent Document 4 can be actually applied is limited to a CaO—TiO2 based oxide. Particularly, it was difficult to integrate the dielectric layer and the magnetic layer even if using the bonding material disclosed in the Patent Document 4 when the material of the dielectric layer is a SrO—TiO2 based oxide or a ZnO—TiO2 based oxide.
In the Patent Document 5, only a varistor composed mainly of ZnO is exemplified as the dielectric. In other words, it is unknown whether the technique described in the Patent Document 5 can be applied even when dielectrics other than the varistor composed mainly of ZnO are used. Further, in general, linear expansion coefficients are greatly deviated between ZnO and ferrite. Therefore, a crack is easily generated at the time of sintering when using the varistor composed mainly of ZnO as the dielectric and the ferrite as the magnetic components even if the intermediate material layer described in the Patent Document 5 is interposed. In addition, a demand for lowering height of a device cannot be satisfied when the thickness of the intermediate layer is thickened to reduce the influences caused by the great deviation of linear expansion coefficient.
The intermediate material layer used in the conventional arts described in the Patent Documents 1 to 5 have an effect of integrally firing the dielectric ceramic and the magnetic ceramic exemplified in each of the documents. However, appearances of a mutual diffusion between the dielectric ceramic and the intermediate material layer and a mutual diffusion between the intermediate material layer and the magnetic ceramic vary greatly depending on the materials of the dielectric ceramic and magnetic ceramic joined to the intermediate material layer. It is necessary to adjust the composition of the intermediate material layer by the dielectric ceramic and magnetic ceramic to control the mutual diffusions appropriately.    Patent Document 1: Japanese Patent Application Publication No. H7-120605    Patent Document 2: Japanese Patent No. 3368671    Patent Document 3: Japanese Patent No. 4020886    Patent Document 4: Japanese Patent No. 4257711    Patent Document 5: Japanese Patent No. 4759584